Field of the Invention
This invention relates to display and illumination fields, and in particular, it relates to an LED (light emitting diode) unit module, light emitting device, and light source system.
Description of Related Art
Conventional high power illumination devices and lighting apparatus typically uses metal halide discharge lamps as the light sources. Because metal halide discharge lamps are white light sources, when color lights are required, various filter plates are placed in front of the metal halide discharge lamps to generate various color output lights. This type of light sources have the disadvantage that the life of metal halide discharge lamps is low, typically from a few hundred to a few thousand hours; also, color lights generated by filter plates have low color saturation and does not give bright colors, and the colors are not rich.
High power light emitting diodes (LED) has the advantages of safe, non-polluting, and long life, and hence have gradually become the first choice in light illumination applications. Their lives can be as long as a hundred thousand hours. Currently, high power LED as stage lighting sources have been realized; they have the advantages of long life, safe and non-polluting, and high color saturation. However, current single LED chips are limited in their light flux; to achieve high brightness color light, typically multiple LED chips of different colors are arrayed to generate high brightness output light.
A commonly used design uses dichroic plates to achieve wavelength-based combination of light generated by red (R), green (G) and blue (B) primary color LED arrays. However, because the spectra of different color lights may partially overlap, and because the transmission curve of the filter plates often cannot be made sufficiently steep due to limitations in fabrication process and cost, wavelength-based light combination can cause light loss due to filtering in the overlapped spectral regions. In particular, when supplemental LED of certain colors are added into the light source system to improve color rendering index, dichroic filters may filter out some important spectral ranges, resulting in relatively large light loss and lower color rendering index of the system.
To solve this problem, another commonly used design is to arrange LED chips of red (R), green (G), blue (B) and white (W) colors in an interleaved pattern to form an array, as shown in FIG. 1. FIG. 1 schematically illustrates an LED array in a conventional technology. This design uses geometry-based light combination to avoid loss of light in certain spectral ranges. However, in this design, because each LED chip requires a corresponding collimating device, the LED chips of different colors are separated from each other by a distance. The different spatial positions cause the output light beams of different colors to have different spatial distributions. Even after light mixing by downstream optical components, the projected light spots still have the problem of non-uniform distribution at positions off of the focal plane.